copy-up · shipping · also copy up, OverlayFS copy-up

Copy-up (OverlayFS)

Copy-up creates an upper-layer counterpart for a lower-layer object when an OverlayFS operation requires it.

Related Observatory article: Copy-up (OverlayFS) on hesela.com

Writable opens, metadata changes and hard-link creation can trigger copy-up. Metadata-only copy-up can defer regular-file data, so an upper entry is not proof that its payload has moved. [1]

Linux v6.12 tries cloning before copying file data. A new upper file therefore need not have independently allocated data blocks. A truncating open can set the transferred length to zero; copy-up is not an archival preservation operation. [2]

Relations

related
OverlayFS, Metadata-only copy-up

Advantages

  • Allows changes through the upper layer without rewriting the lower object.

Limitations

  • The operation and configured features determine which metadata and data move.
  • An upper-layer counterpart is not by itself a complete backup.

Citations

  1. Linux 6.12: Overlay Filesystem, non-directories and metadata-only copy-up (accessed 2026-11-04)
  2. Linux v6.12: OverlayFS copy-up eligibility, data transfer and truncation (accessed 2026-11-04)
Sources & caveats
  • Source review of Linux 6.12 documentation and implementation; no mounted-overlay, restore or crash experiment.

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Hesela team. Copy-up (OverlayFS). Hesela. 2026-11-04. https://hesela.dev/terms/copy-up/